1. Field of the Invention
The present invention relates to a driving system of a backlight of a Liquid Crystal Display (LCD) and, more particularly, to an LCD driving system having Light Emitting Diodes (LEDs) for driving a backlight of an LCD using a plurality of LEDs as a light source.
2. Description of the Related Art
Cold Cathode Fluorescent Lamps (CCFLs), which have been used as a light source for the existing LCD backlight unit, are prone to environmental pollution with use of mercury gas, have slow response rate and low color reproducibility, and are inappropriate for miniaturization of LCD panels.
On the other hand, LEDs are environmentally friendly, possible in high speed response in nanoseconds, which is effective for a video signal stream, and possible in impulsive driving. In addition, it has color reproducibility of over 100% and can be varied in luminance, color temperature, etc. by adjusting the light amounts of red, green and blue LEDs. Moreover, LED light sources are suitable for miniaturization of LCD panels. Due to these merits, LEDs have been actively adopted as a light source for backlight for LCD panels, etc.
When LED arrays with a plurality of LEDs connected in series are used in an LCD backlight, a driving system is required to provide a predetermined constant current to the LED arrays. FIG. 1 is a configuration view illustrating a conventional LCD backlight driving system having LEDs.
Referring to FIG. 1, the conventional LCD backlight driving system includes an SMPS 11, a driving board 12, and a light source 13. The SMPS converts an externally supplied AC voltage to a DC voltage. The driving board 12 includes a plurality of red, green and blue LED DC-DC converters 121, 122 and 123 for converting the DC voltage, converted by the SMPS 11, to a DC voltage suitable for driving respective color LED arrays, and includes red, green and blue constant current controllers 124, 125 and 126 for regulating the DC voltage converted by the DC-DC converters 121, 122 and 123 to maintain a regulated current supplied to the respective color LED arrays. The light source 13 includes a substrate 131 and the respective color LED arrays suitably arranged on the substrate 131, thereby producing white light from the mixture of the light beams from the LED arrays. The conventional LCD backlight driving system further includes a sensor 14 for detecting the luminance and/or color of the light emitted from the light source 13 and a micro-controller 127 provided in the driving board 12 for determining the outputs of the red, green and blue LEDs so as to conform the luminance and/or color of the light detected from the sensor 14 with predetermined luminance and/or color of light.
In such a conventional LCD backlight driving system, after the SMPS 11 converts the AC voltage to the DC voltage at an AC-DC converter 111, the converted DC voltage is converted again to a predetermined value of DC voltage at the DC-DC converter 112. Then, the DC voltage outputted from the DC-DC converter 112 of the SMPS 11 is stepped-up or down transformed to a voltage suitable for driving the corresponding color LED array in the respective LED DC-DC converters 121, 122 and 123. Therefore, in the conventional LCD driving system, similar operations of converting a DC voltage to a DC voltage are redundantly executed, resulting in inefficiency of the system and an increased number of components for the operations. Furthermore, each color LED array requires one DC-DC converter in the driving board 12, increasing the number of required components and the space for forming the circuit, which is not suitable for miniaturization of the LCD backlight.